[GitHub] [airflow] ashb commented on a change in pull request #13433: Schedule tasks of cleared dags

[GitBox <gi...@apache.org>]

ashb commented on a change in pull request #13433:
URL: https://github.com/apache/airflow/pull/13433#discussion_r551856920



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File path: airflow/jobs/scheduler_job.py
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@@ -1483,37 +1483,46 @@ def _do_scheduling(self, session) -> int:
             # Bulk fetch the currently active dag runs for the dags we are
             # examining, rather than making one query per DagRun
 
-            # TODO: This query is probably horribly inefficient (though there is an
-            # index on (dag_id,state)). It is to deal with the case when a user
+            # This query will violate max_active_runs by exactly one if tasks in
+            # max_active_runs or more DAGs are cleared while another DAG is
+            # running. It is to deal with the case when a user
             # clears more than max_active_runs older tasks -- we don't want the
             # scheduler to suddenly go and start running tasks from all of the
             # runs. (AIRFLOW-137/GH #1442)
-            #
-            # The longer term fix would be to have `clear` do this, and put DagRuns
-            # in to the queued state, then take DRs out of queued before creating
-            # any new ones

Review comment:
       Please keep this comment




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